The present invention relates to magnetoresistive heads and more particularly to a method and system for providing electrostatic discharge protection for magnetoresistive heads, particularly in devices using a flex-on suspension or trace-suspension assembly.
FIG. 1 is a block diagram of a portion of a suspension assembly used in magnetoresistive (MR) technology. Depicted with the suspension assembly 50 is a slider 1 including an MR head 10 used in reading magnetic recording media. Typically, the slider 1 includes a merged head. Thus, the MR head 10 is part of a merged head that also includes a write head. However, for clarity, only the MR head 10 is shown. The MR head 10 includes an MR sensor 30. Typically, the MR sensor 10 is an anisotropic magnetoresistive (AMR) sensor or a giant magnetoresistive (GMR) sensor. The slider 1 also includes pads 42, 44, 46 and 48. Two pads 42 and 44 are used for making electrical contact to the MR sensor 30 from other portions of the suspension assembly 50. The other two pads 46 and 48 may be used in making electrical contact to the write head.
In order to use the MR head 10 in a disk drive, electrical connection is made to the MR sensor 30 via the pads 42 and 44. In some conventional systems, a twisted pair of wires is used to connect to the leads 42 and 44. However, the conventional suspension assembly 50 typically provided in order to couple the MR sensor 30 to the remaining electronics (not shown).
The conventional suspension assembly 50 is preferably used with a flex-on suspension (FOS) developed by Read-Rite Corporation of Milpitas, California, in a trace suspension assembly (TSA), or in a cable on suspension (COS). The conventional suspension assembly 50 has a wireless electrical connection with the MR head 10 that allows for a smaller form factor for the head and head-gimbal assembly.
The conventional suspension assembly 50 typically includes a metal arm (not shown) and typically is mechanically coupled with the slider 1. The conventional suspension assembly 50 includes a first lead 52, a second lead 54, a third lead 56 and a fourth lead 58. Note, however, that the third lead 56 and fourth lead 58 may be omitted if the slider assembly 1 does not include a write head. The leads are typically surrounded by an insulating film 60. The insulating film 60 is typically made of polyimide and includes two layers of kapton. The film 60 generally surrounds the leads 52, 54, 56 and 58. Thus, in the conventional suspension assembly 50 the leads 52, 54, 56 and 58 are typically sandwiched between two layers of film 60. The conventional suspension assembly 50 also includes four head gimbal assembly pads 62, 64, 66 and 68 coupled with the leads 52, 54, 56 and 58, respectively. The leads 52 and 54 are also electrically coupled with the MR sensor 30, preferably through pads 42 and 44. Thus, electrical connection can be made to the MR sensor 30 even when the MR head 10 is sufficiently small for use with current high-density recording media.
During manufacture of the conventional suspension assembly 50, the MR head 10 is tested. Consequently, a testing portion 70 of the conventional assembly is typically provided. The testing portion 70 includes test pads 72, 74, 76 and 78 coupled with leads 82, 84, 86 and 88, respectively, that are on a portion of insulating material. Generally, the insulating material is continuous. Thus, the insulating in the testing portion 70 is generally also made of kapton. The first test pad 72 and the second test pad 76 are coupled with the MR sensor 30 via leads 82 and 84, leads 52 and 54, and pads 42 and 44, respectively. The third test pad 76 and the fourth test pad 78 are coupled with the write head via leads 86 and 88, leads 56 and 58, and pads 46 and 48, respectively. Using the first test pad 72 and the second test pad 74 the MR head 10 is tested. Typically, the testing includes a magnetic test and a quasi-static test. In the quasi-static test, the environment in which the slider 1 will function is simulated and the response of the MR sensor 30 tested. In the magnetic test, the slider 1 is actually flown over a disk and the response of the MR sensor 30 tested. Thus, it can be determined whether the MR head 10 functions prior to providing the conventional suspension assembly 50 to a customer.
Although the conventional suspension assembly 50 functions in FOS and TSA embodiments, one of ordinary skill in the art will readily realize that the conventional suspension assembly 50 and head 10 are subject to failure. During fabrication, the MR sensor 30 is often rendered inoperative. In some cases, losses may be as high as ten to twenty percent. It has been determined that these losses are due to tribo-charging of the film 60 in the suspension assembly 50. As higher density recording media is used, the MR head 10 is built smaller to be capable of reading high-density recording media. As the MR head 10 is reduced in size, more damage to the MR sensor 30 can be caused by smaller transient currents due to electrostatic discharge.
For example, during manufacture, electrical contact is often made to the test pads 72, 74, 76 or 78. When a charged metal fixture touches the test pad 72 or 74, the charge can be transferred to the test pad 72 or 74. The charge on the test pad 72 or 74 could cause a large transient current to flow through the MR sensor 30 as the charge is discharged. The transient current can easily destroy the MR sensor 30. Thus, the MR sensor 30 may be damaged or destroyed due to electrostatic discharge (ESD)
Many conventional systems have been developed for protecting the MR head 10 from damage due to ESD. Some conventional methods connect a very low resistance conductor between the leads 52 and 54 or the leads 82 and 84. The conductor typically has a resistance of only a few ohms or less. In other words, the leads 52 and 54 or 82 and 84 are shorted. As a result, the transient current can be prevented. Other conventional methods connect a very high resistance shunt between the leads 52 and 54 or the leads 82 and 84, or between one of the leads 52, 54, 82 or 84 and ground. The high resistance shunt is typically on the order of 106 Ohms. The high resistance shunt allows any charge accumulated on the conventional suspension assembly 50 to be slowly dissipated. Thus, the MR sensor 30 may be preserved.
Although the very high resistance and very low resistance shunts can function, one of ordinary skill in the art will readily recognize that such shunts are typically temporary and, therefore, removable. For example, refer to FIG. 2, which depicts a conventional suspension assembly 50xe2x80x2 described in co-pending U.S. patent application Ser. No. 08/055,729 entitled xe2x80x9cSHORTING BAR AND TEST CLIP FOR PROTECTING MAGNETIC HEADS FROM DAMAGE CAUSED BY ELECTROSTATIC DISCHARGE DURING MANUFACTURExe2x80x9d and assigned to the assignee of the present invention. Also depicted is the slider 1 and MR head 10. Most of the components of the conventional suspension assembly 50xe2x80x2 are the same as those of the conventional assembly 50, depicted in FIG. 1. Consequently, the components are labeled similarly to the conventional suspension assembly 50. For example, the MR head 10xe2x80x2 in the conventional suspension assembly 50xe2x80x2 corresponds to the MR head 10 in the conventional suspension assembly 50.
The conventional suspension assembly 50xe2x80x2 includes a low resistance conductive shunt 92 on an insulating material 90 that is coupled with the testing portion 70xe2x80x2. Typically, the insulating material 90 is an additional piece of kapton that is generally made by lengthening the insulating material for the testing portion 70xe2x80x2. The kapton 90 is flexible and can be folded over to bring the shunt 92 in contact with the test pads 72xe2x80x2, 74xe2x80x2, 76xe2x80x2 and 78xe2x80x2. Usually, the shunt 92 is sufficiently long to short at least the test pads 72xe2x80x2 and 74xe2x80x2 which lead to the MR sensor 30. A clip (not shown) holds the shunt 92 in place during use to ensure that electrical contact is made between the shunt 92 and the test pads 72xe2x80x2 and 74xe2x80x2. Thus, in order to provide protection from ESD induced damage, the insulating material 90 is folded at joint 94 to bring the shunt 92 into contact with the test pads 72xe2x80x2 and 74xe2x80x2 and clipped in place. Once the shunt 92 is in contact with the test pads 72xe2x80x2 and 74xe2x80x2, the MR sensor 30 is protected from electrostatic discharge. When manufacture is complete, the clip can be removed to allow the MR sensor 30 to operate. Furthermore, the kapton 90 and shunt 92 may be cut off at the joint 94. Other conventional shunts operate similarly in that they too are typically temporary and removed prior to use. For example, the test pads 72xe2x80x2 and 74xe2x80x2 or the leads 52 and 54 coupled with the MR sensor 30 may be shorted by a solder bar which is removed when manufacture has completed.
Although the conventional suspension assembly 50xe2x80x2 functions adequately for its intended purpose, one of ordinary skill in the art will readily see that the conventional suspension assembly 50xe2x80x2, as well as other conventional mechanisms for protecting the MR head 10 from ESD damage are temporary. Prior to contacting the shunt 92 with the test pads 72xe2x80x2 and 74xe2x80x2, the MR sensor 30 is not protected. Similarly, once the clip holding the shunt 92 in place is removed, the shunt 92 no longer protects the MR sensor 30 from damage. Thus, the MR head 10 may still be subject to failure due to ESD induced damage during manufacture.
Accordingly, what is needed is a system and method for providing ESD protection for MR heads during fabrication. The present invention addresses such a need.
A method and system for protecting a magnetoresistive (MR) head from electrostatic discharge damage is disclosed. The MR head includes an MR sensor having a first end and a second end. The MR head is coupled with a suspension assembly including a first lead coupled with the first end of the MR sensor, a second lead coupled with the second end of the MR sensor, and an insulating film supporting first and second portions of the first and second leads. In one aspect, the method and system include providing first and second test pads coupled with the first and second leads, respectively. The first and second test pads are for testing the MR head. The method and system also include providing a permanent resistor coupled to the first and second test pads. The permanent resistor has a resistance of less than approximately ten thousand ohms. The permanent resistor also does not adversely affect the functionality of the MR sensor because the resistance of the MR sensor is sufficiently large. In another aspect, the suspension assembly includes first and second head gimbal assembly pads coupled to the first and second leads, respectively. In this aspect, the method and system include coupling a permanent resistor coupled to the first and second head gimbal assembly pads. In another aspect, the MR head is included in a slider having first and second pads for providing current to the MR sensor. In this aspect, the method and system include coupling a permanent resistor to the first and second pads.
According to the system and method disclosed herein, the present invention provides greater robustness against damage due to electrostatic discharge.